The invention relates generally to automatic transport systems, and deals more particularly with an improved automatic transport system of the type having a guide portion which slopes downwardly and free traveling carriers which ride on the guide portion, the improvement comprising a device which limits the forward travel of the carriers on the downwardly sloping guide portion and on other non-sloping guide portions.
Automated transport systems of the type with which this invention is concerned may be used in a garment making plant to carry workpieces to a series of work stations where various work operations are performed or to storage sites. Such a transport system is disclosed in U.S. Pat. No. 4,615,273 filed 12-19-84 by Roald Paul Nymark and Harold Osthus, assigned to the assignee of the present invention and hereby incorporated by references as part of the present disclosure. The aforesaid system is highly automated and includes free traveling trolleys which carry workpieces and a rail network on which the trolleys ride, which network comprises a main rail and subsidiary rail loops. The main rail guides the trolleys to the subsidiary rail loops and the subsidiary rail loops guide the trolleys to and from the work stations or serve as storage sites. The rail network also includes an endless, moving chain adjacent the main rail and pushers attached thereto and spaced along the chain to engage the trolleys and propel them along the main rail and switches for transferring the trolleys to and from the subsidiary rail loops.
Each of the subsidiary loops has a gap adjacent the main rail and, likewise, the main rail has a gap adjacent each subsidiary loop, and the associated switch comprises a short section of rail and an actuator apparatus which is capable of moving the rail section from a first position bridging the gap in the main rail to a second position bridging the gap in the subsidiary loop and vice versa. To switch a trolley from the main rail to a subsidiary rail loop, the rail section is initially located in the gap of the main rail and receives a trolley propelled by a pusher. Then, the actuator apparatus moves the rail section, while the trolley is received on it, to the gap in the subsidiary loop and the pusher propels the trolley onto a rail of the subsidiary rail loop.
Another trolley and rail system comprises a main rail, subsidiary rail loops, and a switch adjacent each subsidiary loop, free traveling trolleys which ride on the rails, pushers for the trolley. Each switch comprises a pair of pivoting fingers having their pivot axis on the main rail. When both pivoting fingers are closed, a trolley is guided over the switch along the main rail and, when one pivoting finger is opened, a trolley is guided toward or received from the subsidiary loop.
In both types of trolley and rail systems described above, a computer is utilized to control the routing of the trolleys to the subsidiary loops and does so in part by controlling the switching mechanisms associated with them. To perform a proper switching operation, the movement of the switch must be timed with the arrival of the designated trolley, and the computer estimates the position of the trolley primarily from the location of its pusher. With either type of switch described above, and with other types of switches, there are discontinuities in either the main rail or the subsidiary loop at all times which discontinuities make it possible for a trolley to inadvertently fall off the rail network.
To compound the problem, it is sometimes advantageous to locate subsidiary loops used for storage several feet above the floor to conserve workspace so that the space beneath the storage loops can be used for work stations, other storage sites, walkways, or other purposes in which case at least one portion of the rail network slopes upwardly and at least one portion slopes downwardly. Also, such automated transport systems may occupy two floors of a factory in which case at least one portion of the rail network slopes upwardly and at least one portion slopes downwardly to link the two floors. If a free traveling, unrestricted trolley rides on such a downwardly sloping portion of a rail network, the trolley rolls ahead of its pusher and descends along the sloping rail portion to the rear of the next pusher, typically 3-5 feet downstream. If the downwardly sloping rail portion is located just upstream of a switch scheduled to divert the trolley, and the pusher does not catch up to the trolley before reaching the switch, the trolley may roll past the switching mechanism before the computer directs the switch to move to the subsidiary loop and hence avoid the switching operation. Also, it is possible in the patent pending system for the trolley immediately in front of the errant trolley to be scheduled to divert to the subsidiary loop and for the errant trolley to fall off the rail through the gap left when the switching mechanism attempts to switch the trolley in front, or for the errant trolley to be inadvertently switched later on to an unscheduled work station or storage site or to jam the system.
There are other factors besides the downward slope of a rail portion which cause a trolley to advance ahead of its pusher and potentially cause problems of the types described above. For example, an air draft from an open door or window may act upon garments suspended from the trolley as a wind acts on a sail, a person may inadvertently brush against a trolley or the associated workpieces, or an operator loading a trolley onto the rail may inadvertently push the trolley forward.
Accordingly, a general aim of the present invention is to improve a transport system of the type having free traveling carriers, a guide for the carriers, and pushers for the carriers so that the carriers cannot advance much ahead of their associated pushers when urged in that direction by gravity or other external force.
A more specific aim of the invention is to provide such an improvement which is simple in construction and use and does not appreciably interfere with the routing of carriers through the system.
Other aims and advantages of the invention will become apparent from the following detailed description and accompanying drawings.